Slip composition for the manufacture of a part in ceramic matrix composite material

Abstract

The invention relates to a slip composition for manufacturing a ceramic matrix composite part comprising: - a carrier liquid, - silicon carbide powder suspended in the carrier liquid, with a concentration between 50% and 77.5% by volume, - carbon powder suspended in the carrier liquid, with a concentration between 7.5% and 40% by volume, - boron-containing powder suspended in the carrier liquid, with a concentration between 5% and 20% by volume, preferably between 5% and 15% by volume, - the total volume percentages of ceramic powder, carbon powder, and boron-containing powder being equal to 100%. (Figure for abbreviation: no figure)

Description

Title of the invention: SLUDGE COMPOSITION FOR THE MANUFACTURE OF A PART IN CERAMIC MATRIX COMPOSITE MATERIAL

[0001] The present invention relates to a slip composition for the manufacture of a part in ceramic matrix composite material.

[0002] The invention finds a particularly advantageous application in the manufacture of ceramic matrix composite (CMC) parts integrated into the hot sections of an aircraft turbomachine, such as combustion chamber walls, turbine blades, or distributors. The invention can be applied in other fields, for example, in the field of industrial gas turbines.

[0003] Indeed, CMC materials are known to possess both good mechanical properties allowing their use for structural elements and the ability to retain these properties at high temperatures.

[0004] CMC materials comprise a fibrous preform made of refractory fibers, in particular carbon or ceramic, which is densified by a ceramic matrix, for example based on silicon carbide SiC.

[0005] A known process for manufacturing parts from CMC material is described in document US2019337859. This process includes a step of producing a fibrous preform from carbon fibers or silicon carbide (SiC).

[0006] The process then includes a step of consolidating the fibrous preform by chemical gas infiltration (CVI) of silicon carbide. The fibrous preform is held in the forming tooling during the CVI. The reactive gases decompose on the surface of the fibers to produce silicon carbide. The silicon carbide thus obtained (SiC / CVI) consolidates the fibrous preform.

[0007] The process includes a step of impregnating the fibrous preform with a slurry containing a suspended silicon carbide (SiC) powder ("Slurry Cast" or "Slurry Transfer Molding" according to Anglo-Saxon terminology). The impregnation step is carried out by injecting a loaded slurry into the fibrous preform under pressure. The slurries used are lightly loaded in order to exhibit, in particular, a stable viscosity (rheo-thinning index > 0.7) and a low viscosity (< 100 mPa·s) for the transport of fillers within the volume of the fibrous preform.

[0008] The process also includes a step of infiltrating the fibrous preform with a molten silicon-based composition so as to form a ceramic matrix. This densification process is known as the MI process ("Melt Infiltration" according to Anglo-Saxon terminology).

[0009] The manufacture of CMC material is conventionally carried out using a slurry of submicron silicon carbide powders to generate the granular matrix during the Slurry Cast process. The slurry makes it possible to obtain a granular network with characteristics compatible with the MI densification cycle. However, the formulation of this suspension is difficult to repeat and not very stable over time due to the rapid evolution (within a few hours) of the slurry's particle size and rheological characteristics.

[0010] Furthermore, the use of most silicon carbide powders in the slip increases the level of reactivity during the liquid silicon infiltration step. Indeed, the liquid silicon tends to react with the carbon in the SiC / CVI layer, which deteriorates the SiC / CVI layer and therefore increases the scrap rate of parts made from a CMC material.

[0011] Figure 1 thus shows the fibers 1 of the fibrous preform covered by a layer of SiC / CVi 2 and the granular matrix 3 of SiC powder obtained during the Slurry Cast process. This figure highlights a zone 4 of the SiC / CVI layer attacked by the liquid silicon during the MI densification step.

[0012] It is known to add carbon to the slip composition in order to limit the reactivity of liquid silicon with the carbon in the SiC / CVI layer. However, such a solution is not satisfactory, since the reactivity of liquid silicon with carbon leads to the creation of large particles that prevent good filling of the granular matrix during the MI densification step.

[0013] The invention aims to effectively overcome the aforementioned drawbacks by proposing a slurry composition for the manufacture of a ceramic matrix composite part comprising: - a carrier liquid, - a silicon carbide powder suspended in the carrier liquid with a concentration between 50% and 77.5% by volume of powder, preferably between 72.5% and 77.5% by volume of powder, - a carbon powder suspended in the carrier liquid with a concentration between 7.5% and 40% by volume of powder, preferably between 7.5% and 22.5% by volume of powder, and - a boron-based powder suspended in the carrier liquid, comprising between 5% and 20% by volume of powder, preferably between 5% and 15% by volume of powder, - the total of the percentages by volume of ceramic powder, carbon powder and boron species powder being equal to 100%.

[0014] The invention thus makes it possible, through the addition of boron-containing powder and carbon powder, to obtain a stable composition while significantly reducing the action of liquid silicon on the SiC / CVI layer due to the carbon saturation of the liquid silicon and also the formation of SiBx species, which slows the attack of the liquid silicon on the SiC / CVI layer. Furthermore, the choice of the characteristics of the powder particles (size and distributions) and of organic additives (dispersant, binder, plasticizer, antiwetting agent) allows control of the pore size of the granular network and the packing ratio in order to optimize the filling of the silicon carbide matrix during the molten silicon infiltration step.

[0015] According to one embodiment of the invention, the silicon carbide powder, the carbon powder and the boron species powder each exhibit a unimodal distribution.

[0016] According to one embodiment of the invention, a ratio between a median size of carbon and boron particles (d50C / B) divided by a median size of silicon carbide particles (d50SiC) is less than 1.5.

[0017] According to one embodiment of the invention, a particle size range of ceramic powder, carbon powder and boron species powder is as follows: 0.1 < dlO < 0.5 qm, 0.5 < d50 < 1.5 qm, preferably 0.5 < d50 < 1 qm, and d90 < 2 qm preferably d90 < 1.5 qm.

[0018] According to one embodiment of the invention, the carrier liquid is water. Alternatively, the carrier liquid is a mixture of water and alcohol, for example ethanol or alcohol alone.

[0019] According to one embodiment of the invention, the slip composition comprises a polyelectrolyte type dispersant having a mass average molar mass Mw greater than or equal to 20000 g / mol.

[0020] According to one embodiment of the invention, the slip composition comprises an organic binder chosen for example from the following products: polyvinyl alcohol (PVA), polyethylene glycol (PEG), glycerol, PolyvinylPyrrolidone (PvP).

[0021] According to one embodiment of the invention, the slip composition comprises a plasticizer having an average molar mass by mass (Mw) less than or equal to 1000 g / mol.

[0022] According to one embodiment of the invention, the slip composition comprises a wetting agent based on a solution of alkylol ammonium salt of a polyfunctional polymer.

[0023] According to one embodiment of the invention, the filler content is between 15% and 25% by volume of slip.

[0024] The invention also relates to a method for manufacturing a ceramic matrix composite part comprising: - a step in creating a fibrous preform from carbon fibers or silicon carbide, - a consolidation step of a fibrous preform carried out by gas-phase chemical infiltration of silicon carbide, - a step of impregnating the fibrous preform with a slip having a composition as previously defined, and - a step of infiltrating the fibrous preform with a molten silicon-based composition in order to form a ceramic matrix.

[0025] The present invention will be better understood and other features and advantages will become apparent upon reading the following detailed description, which includes embodiments given by way of illustration with reference to the accompanying figures, presented by way of non-limiting examples, which may serve to complete the understanding of the present invention and the explanation of its implementation and, where appropriate, contribute to its definition, on which:

[0026] [Fig-1] Fig. 1, already described, is a microscopic view of a section of a part CMC obtained by a process according to the state of the art highlighting the attack of the SiC / CVI layer by liquid silicon during the MI densification step;

[0027] [Fig.2] Fig.2 is a diagram of the different stages of a process of manufacturing a CMC part;

[0028] [Fig. 3a] Fig. 3a shows graphical representations, as a function of a rate shear strength, an upper limit, a lower limit and an average viscosity of a first embodiment of the slip composition according to the invention,

[0029] [Fig. 3b] Fig. 3b is a micro-tomographic cross-sectional view of the CMC object after the step of impregnating the fibrous preform with the slip composition according to the first embodiment of the invention;

[0030] [Fig. 3c] [Fig. 3c] is a micro-tomographic cross-sectional view of the CMC object after MI densification by liquid silicon of the granular network obtained with the slip composition according to the first embodiment according to the invention;

[0031] [Fig.3d] [Fig.3e] Figures 3d and 3e show cross-sectional views of a CMC part obtained with the slip composition according to the first embodiment of the invention respectively opposite the feed and liquid silicon feed side during the MI densification step;

[0032] [Fig.4a] Fig.4a shows graphical representations, as a function of a rate shear strength, an upper limit, a lower limit and an average viscosity of a second embodiment of the slip composition according to the invention,

[0033] [Fig. 4b] [Fig. 4b] is a micro-tomographic cross-sectional view of the CMC object after the step of impregnating the fibrous preform with the slip composition according to the second embodiment of the invention;

[0034] [Fig.4c] The [Fig.4c] is a micro-tomographic cross-sectional view of the CMC object after MI densification by liquid silicon of the granular network obtained with the slip composition according to the second embodiment of the invention;

[0035] [Fig. 4d] [Fig. 4e] Figures 4d and 4e show cross-sectional views of a CMC part obtained with the slurry composition according to the second embodiment of the invention, respectively on the side opposite the feed and on the side fed with liquid silicon following the ML densification step

[0036] It should be noted that identical, similar, or analogous elements retain the same reference from one figure to another.

[0037] Fig. 2 shows the different stages of a process for manufacturing parts in CMC material including a stage 100 of producing a fibrous preform from carbon fibers or silicon carbide (SiC).

[0038] The process then includes a step 101 of consolidation of the fibrous preform carried out by chemical gas infiltration (CVI) of SiC. The fibrous preform is held in the shaping tooling during the CVI.

[0039] The process includes a step 102 of impregnating the fibrous preform with a slurry containing a suspended silicon carbide (SiC) powder ("Slurry Cast" or "Slurry Transfer Molding"). The impregnation step is carried out by injecting the loaded slurry under pressure into the fibrous preform.

[0040] The process also includes a step 103 of infiltrating the fibrous preform with a molten silicon-based composition so as to form a ceramic matrix. This densification process is known as the MI ("Melt Infiltration") process.

[0041] The slip composition used in the "Slurry Cast" process comprises: - a carrier liquid, - a silicon carbide powder suspended in the carrier liquid, comprising between 50% and 77.5% by volume of powder, preferably between 72.5% and 77.5% by volume of powder, - a carbon powder suspended in the carrier liquid comprising between 7.5% and 40% by volume of powder, preferably between 7.5% and 22.5% by volume of powder, - a boron species powder suspended in the carrier liquid comprising between 5% and 20% by volume of powder, preferably between 5% and 15% by volume of powder, - the total of the percentages by volume of ceramic powder, carbon powder and boron species powder being equal to 100%.

[0042] Preferably, the carrier liquid is water. Alternatively, the carrier liquid is a mixture of water and alcohol, for example ethanol or alcohol alone.

[0043] The carbon can be amorphous carbon, graphite or diamond, alone or in mixture.

[0044] The boron species can be boron, boron carbide B4C, or silicon boride (SiB3 or SiB6) alone or in mixture.

[0045] Advantageously, silicon carbide powder, carbon powder and borate species powder each exhibit a unimodal distribution, that is to say that the diameter distribution of each powder advantageously exhibits a single peak located at the median particle size (d50).

[0046] Carbon powder and boron powder also exhibit a particle size distribution equivalent to that of silicon carbide powder. The ratio of the median particle size of carbon and boron (d50C / B) to the median particle size of silicon carbide (d50SiC) is less than 1.5 (d50C / B / d50SiC ratio < 1.5). Such a particle size distribution helps to limit the particle packing rates within the granular matrix.

[0047] A particle size range of ceramic powder, carbon powder and boron species powder is advantageously the following: 0.1 < dlO < 0.5 qm, 0.5 < d50 < 1.5 qm, preferably 0.5 < d50 < 1 qm and d90 < 2 qm, preferably d90 < 1.5 qm. - dlO being the cumulative distribution percentage of 10% of particles having a diameter less than a given value between 0.1 and 0.5 µm, - d90 being the cumulative distribution percentage of 90% of particles having a diameter less than a given value of 2 micrometers, and - d50 being a median particle size corresponding to a cumulative distribution percentage of 50% of particles having a diameter less than a given value between 0.5 and 1 µm.

[0048] The organic additives of the slip (dispersant, binder, plasticizer) are chosen to be soluble in water. The dispersant / binder system is chosen to ensure sufficient steric hindrance between the particles to limit granular stacking, in particular to a stacking ratio of less than or equal to 55% by volume, and thus ensure a good level of aeration of the granular matrix.

[0049] Preferably, the slip composition comprises a polyelectrolyte-type dispersant having a mass-average molar mass Mw greater than or equal to 20,000 g / mol. The dispersant is chosen, for example, from the following products: Polyethyleneimine (PEI) having a mass-average molar mass Mw equal to 25,000 g / mol, Dolapix PC 21 (trade name), PvP (polyvinylpyrrolidone), etc. polyacrylate which may be Darvan 821A (trade name), Darvan CN (trade name), Dolapix A88 (trade name), Dolapix CE64 (trade name).

[0050] Furthermore, the organic binder is chosen for example from the following products: polyvinyl alcohol (PVA), polyethylene glycol (PEG), glycerol, PolyvinylPyrrolidone (PvP).

[0051] The plasticizer has a mass average molar mass (Mw) less than or equal to 1000 g / mol. The plasticizer is, for example, polyethylene glycol (PEG) of the type PEG 200 having a mass average molar mass equal to 200 g.mol-1.

[0052] The slip composition also includes a wetting agent based on an alkyl ammonium salt solution of a polyfunctional polymer, such as DisperBYK 181 (trade name, see technical data sheet https: / / www.byk.com / en / products / additive-guide / disperbyk-181) or any other equivalent product.

[0053] The filler content is between 15% and 25% by volume of the slip. The fillers consist of the active components (powders, binder, plasticizer, dispersant and wetting agent) of the slip.

[0054] According to a first embodiment, the slip composition having a filler content of 20% comprises a carrier liquid consisting of water, silicon carbide powder at a level of 75% by volume of powder, carbon powder at a level of 15% by volume of powder, and boron powder at a level of 10% by volume of powder.

[0055] The particle size range of ceramic powder, carbon powder and boron species powder is as follows: dl0 = 0.40 qm, d50 = 0.86 qm, and d90 = 1.63 pm.

[0056] The binder is PEG 10000, the weight of which is equal to 1% of the total weight of all the powders.

[0057] The plasticizer is PEG200, the weight of which is equal to 1% of the total weight of all the powders.

[0058] The dispersant is PEI, the weight of which is equal to 1.4% of the total weight of all the powders.

[0059] The wetting agent is DisperBYK 181, the weight of which is equal to 0.6% of the total weight of all the powders.

[0060] The jar-turning time TJ is 72 hours. The time TJ corresponds to the duration of the deagglomeration phase, which consists of dispersing the particles in the suspension. In this case, a jar is used in which 33% slip, 33% silicon carbide (SiC) beads (for example, with a diameter of 10 mm), and 33% empty space are mixed by volume. The system is positioned on a rotating means (the jar turner) to ensure mixing of the system at a speed between 20 and 100 rpm. This mixing lasts 72 hours and allows the correct particle size distribution and viscosity of the suspension to be achieved.

[0061] Figure 3a shows graphical representations, as a function of a shear rate Te, of a viscosity V of the slurry having the aforementioned composition. The average viscosity curve Cl of the slurry composition according to the first embodiment lies between an upper limit (curve C2) and a lower limit (curve C3) of viscosity acceptable for the implementation of the "Slurry Cast" process.

[0062] The slip composition has a Shear Thinning Index of 0.73.

[0063] The rheological and granulometric characteristics are repeatable and compatible with good filling of the fibrous preform when implementing the "Slurry cast" process.

[0064] Thus, [Fig.3b] showing the CMC object after the step of impregnating the fibrous preform with the aforementioned slip composition highlights a homogeneous filling of the fibrous preform with a low defect area of ​​0.1%.

[0065] Fig. 3c, showing the CMC object after MI densification, highlights good filling of the granular matrix by liquid silicon with a low defect area of ​​0.18%.

[0066] Figures 3d and 3e are cross-sectional views of a CMC part obtained by a process according to the invention, respectively on the side opposite the liquid silicon feed and on the side receiving the liquid silicon during the MI densification step. These figures show the fibers 1 of the fibrous preform covered by a layer of SiC / CVi 2, as well as the granular silicon carbide matrix 3 obtained during the Slurry Cast process. The white areas 5 correspond to silicon from the densification step.

[0067] Figures 3d and 3e highlight that the aforementioned slip composition prevents the attack of the SiC / CVI layer by the liquid silicon during the ML densification step. The integrity of the SiC / CVI layer is preserved even on the side opposite the liquid silicon feed where the accumulation of metallic impurities (of the aluminium or iron type) along the fibrous preform increases the level of reactivity of the liquid silicon.

[0068] According to a second embodiment, the slip composition having a filler content of 20% comprises a carrier liquid consisting of water, silicon carbide powder at a level of 72.5% by volume of powder, carbon powder at a level of 22.5% by volume of powder, and boron powder at a level of 5% by volume of powder.

[0069] The particle size range of ceramic powder, carbon powder and boron species powder is as follows dl0=0.40 pm, d50 = 0.82 pm, and d90 = 1.47 pm.

[0070] The binder is PEG10000, the weight of which is equal to 1% of the total weight of all the powders.

[0071] The plasticizer is PEG200, the weight of which is equal to 5% of the total weight of all the powders.

[0072] The dispersant is PEI, the weight of which is equal to 1.4% of the total weight of all the powders.

[0073] The wetting agent is DisperBYK 181, the weight of which is equal to 0.6% of the total weight of all the powders.

[0074] The jar-turning time TJ is 72 hours. The time TJ corresponds to the duration of the deagglomeration phase, which consists of dispersing the particles in the suspension. In this case, a jar is used in which 33% slip, 33% silicon carbide (SiC) beads (for example, with a diameter of 10 mm), and 33% empty space are mixed by volume. The system is positioned on a rotating means (the jar turner) to ensure mixing of the system at a speed between 20 and 100 rpm. This mixing lasts 72 hours and allows the correct particle size distribution and viscosity of the suspension to be achieved.

[0075] Figure 4a shows graphical representations, as a function of a shear rate Te, of a viscosity V of the slurry having the aforementioned composition. The average viscosity curve Cl' of the slurry composition according to the invention lies between the upper limit (curve C2') and the lower limit (curve C3') of viscosity acceptable for the implementation of the "Slurry Cast" process.

[0076] The slip composition has a Shear Thinning Index of 0.74.

[0077] The rheological and granulometric characteristics are repeatable and compatible with good filling of the fibrous preform when implementing the "Slurry cast" process.

[0078] Thus, [Fig.4b] showing the CMC object after the step of impregnating the fibrous preform with the aforementioned slip composition highlights a homogeneous filling of the fibrous preform with a low defect area of ​​0.38%.

[0079] Fig. 4c, showing the CMC object after MI densification, highlights good filling of the granular matrix by liquid silicon with a low defect area of ​​0.04%.

[0080] Figures 4d and 4e show cross-sectional views of a CMC part obtained by a process according to the invention, respectively on the side opposite the feed and on the side fed with liquid silicon during the MI densification step. These figures show the fibers 1 of the fibrous preform covered by a layer of SiC / CVi 2, as well as the granular silicon carbide matrix 3 obtained during the Slurry Cast process. The areas 5 correspond to silicon from the densification step.

[0081] Figures 4d and 4e demonstrate that the aforementioned slurry composition prevents the SiC / CVI layer from being attacked by the liquid silicon during the ML densification step. The integrity of the SiC / CVI layer is preserved even on the side opposite the liquid silicon feed, where the accumulation of metallic impurities is possible. aluminum or iron type along the fibrous preform increases the level of reactivity of the liquid silicon.

[0082] Of course, the different features, variants and / or embodiments of the present invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive.

[0083] Furthermore, the invention is not limited to the embodiments described above and provided solely by way of example. It encompasses various modifications, alternative forms and other variants that a person skilled in the art may consider within the scope of the present invention, and in particular all combinations of the different modes of operation described above, which may be taken separately or in combination.

Claims

Demands

1. Slip composition for the manufacture of a ceramic matrix composite part characterized in that said slip composition comprises: - a carrier liquid, - a silicon carbide powder suspended in the carrier liquid comprising between 50% and 77.5% by volume of powder, preferably between 72.5% and 77.5% by volume of powder, - a carbon powder suspended in the carrier liquid comprising between 7.5% and 40% by volume of powder, preferably between 7.5% and 22.5% by volume of powder, and - a boron species powder suspended in the carrier liquid comprising between 5% and 20% by volume of powder, preferably between 5% and 15% by volume of powder, - the total of the percentages by volume of ceramic powder, carbon powder and boron species powder being equal to 100%.

2. Slip composition according to claim 1, characterized in that the silicon carbide powder, the carbon powder and the boron species powder each exhibit a unimodal distribution.

3. Slip composition according to claim 1 or 2, characterized in that a ratio between a median size of carbon and boron particles (d50C / B) divided by a median size of silicon carbide particles (d50SiC) is less than 1.

5.

4. Slip composition according to any one of claims 1 to 3, characterized in that a particle size range of ceramic powder, carbon powder and boron species powder is as follows: 0.1 < dlO < 0.5 qm, 0.5 < d50 < 1.5 qm, preferably 0.5 < d50 < 1 qm, and d90 < 2 qm preferably d90 < 1.5 qm.

5. Slip composition according to any one of claims 1 to 4, characterized in that the carrier liquid is water.

6. Slip composition according to any one of claims 1 to 5, characterized in that it comprises a polyelectrolyte type dispersant having a mass average molar mass Mw greater than or equal to 20000 g / mol.

7. Slip composition according to any one of claims 1 to 6, characterized in that it comprises an organic binder selected for example from the following products: polyvinyl alcohol (PVA), polyethylene glycol (PEG), glycerol, polyvinylpyrrolidone (PvP).

8. Slip composition according to any one of claims 1 to 7, characterized in that it comprises a plasticizer having a mass average molar mass (Mw) less than or equal to 1000 g / mol.

9. Slip composition according to any one of claims 1 to 8, characterized in that it comprises a wetting agent based on an alkylol ammonium salt solution of a polyfunctional polymer.

10. Slip composition according to any one of claims 1 to 9, characterized in that a filler content is between 15% and 25% by volume of slip.

11. A method for manufacturing a ceramic matrix composite part characterized in that it comprises: - a step (100) of producing a fibrous preform from carbon fibers or silicon carbide (SiC), - a step (101) of consolidating a fibrous preform produced by chemical gas infiltration (CVI) of silicon carbide, - a step (102) of impregnating the fibrous preform with a slurry having a composition defined according to any one of the preceding claims, and - a step (103) of infiltrating the fibrous preform with a molten silicon-based composition so as to form a ceramic matrix.

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